1,317 research outputs found
Detection by NMR of a "local spin-gap" in quenched CsC60
We present a 13C and 133Cs NMR investigation of the CsC60 cubic quenched
phase. Previous ESR measurements suggest that this phase is metallic, but NMR
reveals contrasting electronic behavior on the local scale. The 13C
spin-lattice relaxation time (T1) exhibits a typical metallic behavior down to
50 K, but indicates that a partial spin-gap opens for T<50 K. Unexpectedly,
133Cs NMR shows that there are two inequivalent Cs sites. For one of these
sites, the NMR shift and (T1T)^{-1} follow an activated law, confirming the
existence of a spin-gap. We ascribe this spin-gap to the occurrence of
localized spin-singlets on a small fraction of the C60 molecules.Comment: 4 figure
Mechano-Optical Analysis of Single Cells with Transparent Microcapillary Resonators
The study of biophysical properties of single cells is becoming increasingly relevant in cell biology and pathology. The measurement and tracking of magnitudes such as cell stiffness, morphology, and mass or refractive index have brought otherwise inaccessible knowledge about cell physiology, as well as innovative methods for high-throughput label-free cell classification. In this work, we present hollow resonator devices based on suspended glass microcapillaries for the simultaneous measurement of single-cell buoyant mass and reflectivity with a throughput of 300 cells/minute. In the experimental methodology presented here, both magnitudes are extracted from the devices' response to a single probe, a focused laser beam that enables simultaneous readout of changes in resonance frequency and reflected optical power of the devices as cells flow within them. Through its application to MCF-7 human breast adenocarcinoma cells and MCF-10A nontumorigenic cells, we demonstrate that this mechano-optical technique can successfully discriminate pathological from healthy cells of the same tissue type
Guided Modes in Negative Refractive Index Waveguides
We study linear guided waves propagating in a slab waveguide made of a
negative-refraction- index material, the so-called left-handed waveguide. We
reveal that the guided waves in left-handed waveguides possess a number of
peculiar properties, such as the absence of the fundamental modes, mode double
degeneracy, and sign-varying energy ux. In particular, we predict the existence
of novel types of guided waves with a dipole-vortex structure of the Pointing
vector.Comment: 4 pages, 4 figure
Theoretical analysis of the focusing of acoustic waves by two-dimensional sonic crystals
Motivated by a recent experiment on acoustic lenses, we perform numerical
calculations based on a multiple scattering technique to investigate the
focusing of acoustic waves with sonic crystals formed by rigid cylinders in
air. The focusing effects for crystals of various shapes are examined. The
dependance of the focusing length on the filling factor is also studied. It is
observed that both the shape and filling factor play a crucial role in
controlling the focusing. Furthermore, the robustness of the focusing against
disorders is studied. The results show that the sensitivity of the focusing
behavior depends on the strength of positional disorders. The theoretical
results compare favorably with the experimental observations, reported by
Cervera, et al. (Phys. Rev. Lett. 88, 023902 (2002)).Comment: 8 figure
Negative refraction and left-handed behavior in two-dimensional photonic crystals
We systematically examine the conditions of obtaining left-handed (LH)
behavior in photonic crystals. Detailed studies of the phase and group
velocities as well as the phase np and group ng refractive index are given. The
existence of negative refraction does not guarantee the existence of negative
index of refraction and so LH behavior. A wedge type of experiment is suggested
that can unambiguously distiguinsh between cases of negative refraction that
occur when left-handed behavior is present, from cases that show negative
refraction without LH behavior.Comment: 4 pages 4 figures, submitted to Phys. Rev. B Rapid Communication
Protein interactions in Xenopus germ plasm RNP particles
Hermes is an RNA-binding protein that we have previously reported to be found in the ribonucleoprotein (RNP) particles of Xenopus germ plasm, where it is associated with various RNAs, including that encoding the germ line determinant Nanos1. To further define the composition of these RNPs, we performed a screen for Hermes-binding partners using the yeast two-hybrid system. We have identified and validated four proteins that interact with Hermes in germ plasm: two isoforms of Xvelo1 (a homologue of zebrafish Bucky ball) and Rbm24b and Rbm42b, both RNA-binding proteins containing the RRM motif. GFP-Xvelo fusion proteins and their endogenous counterparts, identified with antisera, were found to localize with Hermes in the germ plasm particles of large oocytes and eggs. Only the larger Xvelo isoform was naturally found in the Balbiani body of previtellogenic oocytes. Bimolecular fluorescence complementation (BiFC) experiments confirmed that Hermes and the Xvelo variants interact in germ plasm, as do Rbm24b and 42b. Depletion of the shorter Xvelo variant with antisense oligonucleotides caused a decrease in the size of germ plasm aggregates and loosening of associated mitochondria from these structures. This suggests that the short Xvelo variant, or less likely its RNA, has a role in organizing and maintaining the integrity of germ plasm in Xenopus oocytes. While GFP fusion proteins for Rbm24b and 42b did not localize into germ plasm as specifically as Hermes or Xvelo, BiFC analysis indicated that both interact with Hermes in germ plasm RNPs. They are very stable in the face of RNA depletion, but additive effects of combinations of antisense oligos suggest they may have a role in germ plasm structure and may influence the ability of Hermes protein to effectively enter RNP particles
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